Studies with transgenic (Tg) mouse lines expressing different forms of the prion protein (PrP) support the hypotheses that the amino acid structure of PrP is the main factor determining (1) whether a prion disease requires initiation by prions or is spontaneous, (2) the scrapie incubation time, (3) the characteristics of newly formed infectious prions in a host and (4) the characteristics of the neuropathology. Multiple lines of experimental evidence indicate that the regional accumulation of PrPSc in scrapid, PrPCJD in Creutzfeldt-Jakob disease and PrPGSS in Gerstmann-Straussler syndrome are the direct cause of the clinically significant morphological and/or functional neuronal defects. From the perspective of neuropathology, the rate of formation and anatomic distribution of spongiform degeneration of neurons and nerve cell loss are the pathogenic determinants of incubation time. Furthermore, studies in my laboratory indicate that the rate of accumulation and the rate of spread of PrPSc from region to region in the brain during scrapie correlates with the rate of spread of neuropathology. Tg-mouse lines to be created by Project II of this proposal will incorporate multiple new PrP transgenes with specific amino acid substitutions. Some will mimic Armenian and Chinese hamster and NZW and I/LnJ mouse PrP structure. These animals, along with the Syrian hamster, have been studied extensively by our laboratories because they have markedly different scrapid incubation times. In this project (Project III), we will use a combination of classical neuropathological methods, immunohistochemistry for PrP and GFAP, in situ hybridization with cDNA probes, and newly developed methods for localizing and measuring PrPSc to examine the new PrP transgenic mouse lines. We anticipate an average of 15 new lines each year. These new Tg-mouse lines plus those already on hand promise to help us gain a better understanding of how the amino acid structure of PrP influences specific issues of the pathogenesis of scrapie. In particular, we want to know the relationship of PrP structure to the rate of accumulation of PrPSc, the rate of formation of spongiform degeneration of neurons, and PrP amyloid plaque formation. Additionally, we want to know whether the kinetics of PrPSc accumulation and/or spongiform degeneration best correlates with incubation time.